1. Brief Description of the Invention
This invention pertains in general to the delivery of ultra-pure gases, primarily reactive gases, to a point of use. More specifically, this invention relates to methods and systems to deliver ultra-pure gases which are liquefied at room temperature with a vapor pressure above atmospheric pressure to semiconductor tools and other points of use.
2. Prior Art
Ultra-high purity (UHP) electronics specialty gases (ESG's) are needed for the integrated circuit (IC) manufacturing industry. Typical purity requirements at state of the art manufacturing are 10-100 parts per billion (ppb) for molecular impurities, less than 1 particle/M.sup.3 of size greater than 0.05 micrometer, and 10-1000 parts per trillion (ppt) for metallic impurities, in accordance with the recently published SIA Roadmap.
Because of the increasing size of the wafer fabs, as well as for reasons of cost reduction, quality and safety, it is desired to increase the mass flow rate of the ESG's used on a single manufacturing site. Cost reduction has been attempted frequently in practice by reducing the number of cylinder cabinets on a site and merely increasing the flow rate extracted from ESG storage cylinders, with sometimes application of thermal energy onto the cylinders. However, this solution is of limited capability because imperfect cylinder exchange procedure is a well known practical source of contamination and of its subsequent detrimental consequences.
Moreover, in the case of ultra-pure ESG's which are liquefied at room temperature with a vapor pressure above atmospheric pressure, high mass flow rate gas delivery involves the extraction of a biphasic gas-liquid aerosol from the storage container of pressurized liquid ESG, because the energy of vaporization is difficult to compensate in practice from an external heat source.
An increased mass flow rate extraction of exclusively gas phase ESG is possible by introducing large size containers as a means of bulk storage for delivery of these ESG's, via increased thermal transfer to the pressurized ESG liquid phase due to a larger liquid-gas interface area. The limiting value of pure gas phase supply will depend mostly on flow rate and duration, depending on the specific ESG physical properties and on the container thermo-mechanical properties.
It has been proposed to solve the problem by improving the thermal energy exchange at the evaporating liquid surface and/or by trapping or volatilizing the liquid phase droplets of the aerosol. These means indeed alleviate the problem within an intermediate range of mass flow rates but become insufficient for the exceedingly high mass flow rates needed in modern installations. Also, the perfect removal of the liquid phase droplets is extremely difficult or impossible at such high flow rates.
The undesirable consequences of such biphasic mist extraction for ESG delivery are extremely severe, especially:
1. the loss of the purification phenomenon intrinsic in the evaporation of the pressurized liquid into gas phase; PA1 2. the introduction of liquid phase into devices designed for gas flow control, which cannot function properly under such circumstances; and PA1 3. many ESG's are practically significantly more corrosive in their liquid phase, more so if not of ultra-high purity, and above conditions frequently involve materials corrosion, with the subsequent detrimental consequences on contamination control and safety. PA1 (a) providing a source (preferably a bulk source) of an ultra-high purity liquid, the ultra-high purity liquid having the characteristic of being liquefied at room temperature with a vapor pressure above atmospheric pressure; PA1 (b) transporting (preferably via pressure in source pressure alone which is above atmospheric, although pumping means may be employed in some embodiments) the ultra-high purity liquid from the source to one or more means to effect a phase change of the ultra-high purity liquid to form an ultra-high purity gas at a pressure less than the source pressure; PA1 (c) effecting a phase change (preferably at or near equilibrium vaporization conditions) of the ultra-high purity liquid to form an ultra-high purity gas in the one or more means to effect the phase change, the means to effect the phase change having a means to effect phase change pressure less than the source pressure but higher than the second station (preferably the means to effect phase change pressure is atmospheric pressure); and PA1 (d) routing the ultra-high purity gas from the means to effect the phase change to the second station, the second station preferably at or near a point of use (preferably with no intermediate, potential impurity-generating media between the means to effect the phase change and the second station other than ultra-clean conduit). PA1 (a) a container (preferably a bulk container) adapted to be filled at least partially with ultra-high purity liquid, the ultra-high purity liquid in a container having the characteristic of being liquefied at room temperature with a vapor pressure above atmospheric pressure, the container having mechanical strength to withstand a pressure and temperature sufficient to maintain the ultra-high purity liquid in substantially the liquid phase; PA1 (b) means for transporting the ultra-high purity liquid from the container to one or more means to effect a phase change of the ultra-high purity liquid to form an ultra-high purity gas, the means for transporting having first and second ends, the first end connected to one or more containers of ultra-high purity liquid, and at the second end connected to one or more means to effect phase change; PA1 (c) one or more means to effect phase change connected to the container via the means for transporting, each means to effect phase change comprising means sufficient to vaporize the ultra-high purity liquid (preferably at or near equilibrium vaporization conditions) to form an ultra-high purity gas in the one or more means to effect phase change; and PA1 (d) conduit (preferably ultra-clean) connecting each of the phase change devices to a station distal from the means to effect phase change, preferably a point of use (preferably with no intermediate, potentially impurity-generating media between the phase change device and the point of use other than ultra-clean conduit).
Therefore it would be advantageous for many industries, including the semiconductor manufacturing industry, if high purity, ultra-pure and/or ultra-high purity gases could be delivered to a point of use with avoidance of most or all of these detriments.